Flowmeters of the above type have been known for a number of years, typical examples being shown in U.S. Pat. No. 3,613,449 issued in October 1971 to Soejima et al, U.S. Pat. No. 3,640,135 issued in February 1972 to Tomiyasu et al, and U.S. Pat. No. 3,742,762 issued in July 1973 to Tomiyasu et al. Arrangements such as those shown in the Tomiyasu et al '135 patent, in which the horizontal reaction component is measured, have found the most general acceptance because the magnitude of the horizontal component will not be affected by any build up of residual material adhering to the deflector plate.
Although such flowmeters have considerable utility, they present certain problems in implementation, particularly in obtaining reliable measurement of the horizontal reaction component. The flowmeter necessarily operates in adverse environments, with typical materials being metered having a high dust content, and any mechanical pivots and other sensitive components must be protected from such dust. These problems and other relevant prior art patents are discussed in U. K. Patent Specification No. 2,020,038 (Milltronics) published Nov. 7, 1979, which discloses a flowmeter in which the horizontal component is measured by one or more strain gauge bridges in an arrangement which can be made mechanically substantially immune both from the effects of dust and material build up, and is also insensitive to uneven distribution of material impacting the deflector plate. Such flowmeters perform very satisfactorily, but present the problem that the deflector plate must be housed in a comparatively bulky rectangular housing which must be fabricated and equipped with suitable connecting and adaption hardware to connect its upstream and downstream ends to conduits of vessels, the flow between which is to be monitored. Conduits for fluent materials are commonly cylindrical tubular pipes, which further complicates installation. Even when such an arrangement is arranged at a free outlet of a tubular vessel, and a full enclosure is not required, the adaptor structure required can be quite complex, as is illustrated in U.S. Pat. No. 4,407,380 (Elder), in which a similar device is disposed at the outlet of a screw conveyor. Further examples of the complications entailed in the installation of this type of flowmeter, and its relative bulk, are found on the rear page of the brochure "Milltronics HYFLO (Trade Mark) Solids Flowmeters", published by Milltronics in November 1984.